1. Field of the Invention
The present invention pertains to developing three dimensional velocity models and more particularly to developing three dimensional information from a grid of two dimensional lines.
2. Related Prior Art
U.S. Pat. No. 4,330,872, titled "Common offset Distance Seismic Trace Filtering" issued to Robert H. Bratton relates to a multiple coverage seismic exploration technique that provides for a plurality of seismic trace recordings along a line of exploration. From these recordings, sets of common offset distance traces are gathered. Initial estimates are made of the apparent dips associated with the seismic reflection signals across each set of common offset distance traces. These initial dip estimates are smoothed and the sets of common offset distance traces filtered along the apparent dips associated with the smoothed dip estimates to enhance the signal to noise ratio of primary reflection signals.
U.S. Pat. No. 4,672,545, titled "Method and Apparatus for Synthesizing Three Dimensional Seismic Data", issued to Jia-Wen Lin, et al., relates to a method and apparatus for converting seismic data obtained at known points to synthesized seismic traces obtainable at arbitrarily selected points. Two dimensional seismic data are converted to three dimensional data with the aid of a programmed computer to permit generation of arbitrary views of particular geologic structure as well as a mathematical representation of the structure. In order to provide accurate interpolation from the known data, both apparent and true dip characteristics are obtained for the surveyed structure, and seismic trace data for a desired point are synthesized as a function of the dip of the surveyed structure. The dip characteristics are obtained from partial derivatives of the two dimensional data in specified coordinate directions. A three dimensional surface corresponding to the dip characteristics is obtained by a least squares fitting technique. The data obtained at the known points are weighted both by distance from the desired point and the semblance coefficients associated with dip for these points to synthesize the desired data.
U.S. Pat. No. 4,736,347, titled "Multiple Stacking and Spatial Mapping of Seismic Data", issued to Bernard Goldberg, et al., relates to a method where seismic traces are stacked in a plurality of orthogonal measures to form multiple stacked traces at a positive offset. The stacking process determines the apparent velocities as functions of the travel time at the positive offset. The interval acoustic velocity of the first layer is then determined from knowledge of surface topography, source-receiver offset, two-way travel times and the first reflector apparent velocities. The first layer velocity information enables the incident and emergent angles of the ray paths at the surface to be calculated, as well as enabling the dip angles and spatial coordinates of the reflection points on the first reflecting boundary to be determined.
Seismic data corresponding to the second reflecting boundary are then spatially mapped to the first reflecting boundary by ray tracing and by a new method for calculating the apparent velocities at the first boundary. The process is repeated for each succeedingly deeper boundary. The derived acoustic velocity model of the earth is displayed as a stacked seismic section in spatial coordinates. This process may be applied to obtain earth models and seismic sections in both two and three dimensions.
U.S. Pat. No. 4,866,659, titled "Method for Selection of Mining and Drilling Sites Using Synthesized Three Dimensional Seismic Data", issued to Jia-Wen Lin, et al. relates to a method for converting seismic data obtained at known points to synthesized seismic traces obtainable at arbitrarily selected points. Two dimensional seismic data are converted to dense three dimensional data with the aid of a programmed computer to permit generation of arbitrary views of a particular geologic structure as well as a mathematical representation of the structure. The data is used to locate potential drilling and mining locations for drilling oil or other minerals. In order to provide accurate interpolation from the sparse two dimensional data, both apparent and true dip characteristics are obtained for the surveyed structure, and seismic trace data for a desired point are synthesized as a function of the dip of the surveyed structure. The dip characteristics are obtained from partial derivatives of the two dimensional data in specified coordinate directions. A three dimensional surface corresponding to the dip characteristics is obtained by a least squares fitting technique. The data obtained at the known points are weighted both by distance from the desired point and the semblance coefficients associated with the dip for these points to synthesize the desired data.
U.S. Pat. No. 4,953,140, titled "Method of Subterranean Mapping", issued to Mark A. Dablain, relates to a method for modeling the subterranean structure of the earth. Assumed velocities are used in initially modeling the path of seismic energy through the subterranean structure. Arrays of travel times corresponding to upward and downward going energy from various locations in the subterranean structure are calculated using ray tracing techniques. Actual reflection points are located when the sum of the upward and downward going travel times calculated with respect to a particular point in the structure equals the actual travel times recorded. The velocity assumptions are verified by selecting common reflection point records and adjusting the assumed velocities, such that reflection events on displayed traces from the common reflection point are horizontal. A least squares fit is used to correct the common reflection point event data until it is optimally flat.
U.S. Pat. No. 4,953,142, titled "Model Based Depth Processing of Seismic Data", issued to Daniel H. Rimmer, relates to a model based iterative method of depth processing seismic data. An estimate of a geologic horizon is entered into a three dimensional seismic model and synthetic shot records are determined from the model. Reflection tracks are estimated from the modeling results. The actual seismic traces are sorted into bins according to common reflection points determined from the reflection tracks and are stacked. The sorted and stacked data are used to estimate the difference between the seismic travel time and the model travel time, and the model is changed in order to match the seismic data. The process is repeated until the margin of error is acceptable. Lower horizons of interest are modeled in the same way until all the horizons of interest in a geological area are determined.
U.S. Pat. No. 4,964,097, titled "Three Dimensional Image Construction Using a Grid of Two Dimensional Depth Sections", issued to Shein S. Wang, et al., relates to a method for generating a three dimensional velocity model that makes use of two dimensional depth images, which are the result of two dimensional pre-stack depth migration, and corrects the out of plane distortion by ray tracing through a three dimensional model. The three dimensional model boundaries are iterated until the three dimensional effects ar minimized. The final model can be used for a final three dimensional prestack depth migration, or as a three dimensional interpretation of all the two dimensional depth migration results.
U.S. Pat. No. 4,964,103, titled "Three Dimensional Before Stack Depth Migration of Two Dimensional or Three Dimensional Seismic Data", issued to James H. Johnson, relates to a method of three dimensional before stack depth migration of two dimensional or three dimensional seismic data. Ray tracing is used to move before stack trace segments to their approximate three dimensional position. The trace segments are scaled to depth, binned, stacked and compared to the model The model can then be changed to match the depth trace segments which are stacked better, moved closer to their correct three dimensional position and compare better to the model.
U.S. Pat. No. 4,992,996, titled "Interval Velocity Analysis and Depth Migration Using Common Reflection Point Gathers", issued to Shein S. Wano, et al., relates to a method for performing velocity analysis while eliminating the effects on weak signals caused by strong signals. This method includes migrating each event of the pre-stack trace to a single location instead of all possible locations. This correct location is determined by ray-tracing through a velocity model. The input trace is divided into many windows, and each window is migrated to a place determined by ray-tracing the center of the window through the model. If the velocity model is accurate, each event will be migrated to the proper location yielding an accurate depth section with no migration artifacts. As a by-product, if the model is not accurate, the post-migrated parts (PMP's) provide a clean velocity analysis.